Photoalignment technology allows for fabrication of spatially varying liquid crystal alignment patterns on a photoalignment layer. One of the types of devices that may be fabricated by utilizing such photoalignment technology is a polarization grating (PG).
A PG is a sinusoidal phase grating made of a retardation film with spatially varying optical axis. Unlike other optical gratings, a PG diffracts light into +1 and −1 diffraction orders, while all other higher orders are eliminated. Moreover, a half wave PG has the highest diffraction efficiency among all kinds of diffraction gratings.
Applications for PGs are devices based on diffraction optics. There are left hand PGs and right hand PGs, depending on the handedness of the spatially varying optical axis or axes.
In a conventional process for fabricating a PG using photoalignment, interference between two coherent laser beams having respectively left hand circular polarized light and right hand circular polarized light generates a linear polarized light pattern with spatially varying polarization directions. This linear polarized light pattern is used to expose a photoalignment layer, and thus generate spatially varying liquid crystal alignment pattern on the photoalignment layer.